File:2-Stroke Engine ani.gif|right
A '''two-stroke''' (or '''two-cycle''') '''engine''' is a type of internal combustion engine
which completes a power cycle with two strokes (up and down movements) of the piston
during only one crankshaft revolution. This is in contrast to a "four-stroke engine
", which requires four strokes of the piston to complete a power cycle during two crankshaft revolutions. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust (or Scavenging (automotive)|scavenging
) functions occurring at the same time.
Two-stroke engines often have a high power-to-weight ratio
, power being available in a narrow range of rotational speeds called the "power band". Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts, and so can be more compact and significantly lighter.